15.000 balance on card

if by consolidate you mean balance transfer to another card yes, that is really the best thing to do especially if you have a big balance by transfering the balance most credit companies have promo rates below 5.99% fixed apr so it will save you alot of money and get you out of collections. if you dont have another credit card try and see if you can get approved for a new one many companies have those promo rates on new accounts as well.

If it is on collection it is to late to consolidate it, the only thing you could legally do is now pay those scumbags. Try to negotiate 30-40% of the actual balance, and please do it in writing not over the phone, in writing makes it official .